JS根據獎品權重計算中獎概率

var prizes = ["一等獎","二等獎","三等獎","未中獎"];    //獎項名稱數組

var prizeWeight = [1, 5, 20, 74];    //獎項權重數組，表征各獎項的中獎機會占總數的百分比。比如一等獎的中獎率是1%，二等獎的中獎率是5%   

//設置獎項名稱、權重等數組
var prizes = [
    {"name": "一等獎", "weight": 1}, 
    {"name": "二等獎", "weight": 5}, 
    {"name": "三等獎", "weight": 20}, 
    {"name": "未中獎", "weight": 74}
];

//數組累加求和函數：Array.reduce(function(prev ,cuurentValue), initialValue)
var weightSum = prizeWeight.reduce(function(prev, currVal){    //計算權重之和：1+5+20+74=100
    return prev + currVal;    //prev 是前一次累加後的數值，currVal 是本次待加的數值
}, 0);

//抽獎函數
var lottery = function(weightSum) {
    var res = "未中獎";    //默認設置抽獎結果為“未中獎”
    console.log("本程序的獎項權重和值：", weightSum);
    
    //生成一個權重隨機數，介於0-weightSum之間
    var random = Math.random()*weightSum;    //生成一個權重隨機數（0 到 weightSum 之間）
    console.log("本次抽獎的權重隨機數：", random);
    
    //權重數組重組並排序
    var concatWeightArr = prizeWeight.concat(random);    //將隨機數加入權重數組
    var sortedWeightArr = concatWeightArr.sort(function(a, b){return a-b;});    //將包含隨機數的新權重數組按從小到大（升序）排序
    console.log("含權重隨機數的新權重數組升序排序後：", sortedWeightArr);
    
    //索引權重隨機數的數組下標
    var randomIndex = sortedWeightArr.indexOf(random);    //索引隨機數在新權重數組中的位置
    randomIndex = Math.min(randomIndex, prizes.length -1);    //權重隨機數的下標不得超過獎項數組的長度-1，重新計算隨機數在獎項數組中的索引位置                
    console.log("本次權重隨機數對應的數組下標：", randomIndex);
    
    //取出對應獎項
    res = prizes[randomIndex];    //從獎項數組中取出本次抽獎結果
    console.log("本次抽獎結果：", res);
    
    return {"weightSum": weightSum , "weightRandom": random, prizeIndex: randomIndex, "data": res};    //返回本次抽獎結果
};

//layui 模塊化引用
layui.use(['jquery', 'util'], function(){
    var $ = layui.$, util = layui.util;
    
    //設置獎項名稱、權重、中獎次數等數組
    var prizes = ["一等獎", "二等獎", "三等獎", "未中獎"];    //獎項名稱數組
    var prizeWeight = [1, 5, 20, 74];    //獎項權重數組，表征各獎項的中獎機會占總數的百分比。比如一等獎的中獎率是1%，二等獎的中獎率是5%            
    
    //開發者也可合並聲明獎項名稱、權重等數組在一個對象中
    //var prizes = [
    //    {"name": "一等獎", "weight": 1}, 
    //    {"name": "二等獎", "weight": 5}, 
    //    {"name": "三等獎", "weight": 20}, 
    //    {"name": "未中獎", "weight": 74}
    //];                
    
    //數組累加求和函數：Array.reduce(function(prev ,cuurentValue), initialValue)
    var weightSum = prizeWeight.reduce(function(prev, currVal){    //計算權重之和：1+5+20+74=100
        return prev + currVal;    //prev 是前一次累加後的數值，currVal 是本次待加的數值
    }, 0);
    document.getElementById("weightSum").innerhtml = weightSum;    //設置權重和值
    
    //抽獎函數
    var lottery = function(weightSum) {
        var res = "未中獎";    //默認設置抽獎結果為“未中獎”
        console.log("本程序的獎項權重和值：", weightSum);
        
        //生成一個權重隨機數，介於0-weightSum之間
        var random = Math.random()*weightSum;    //生成一個權重隨機數（0 到 weightSum 之間）
        console.log("本次抽獎的權重隨機數：", random);
        
        //權重數組重組並排序
        var concatWeightArr = prizeWeight.concat(random);    //將隨機數加入權重數組
        var sortedWeightArr = concatWeightArr.sort(function(a, b){return a-b;});    //將包含隨機數的新權重數組按從小到大（升序）排序
        console.log("含權重隨機數的新權重數組升序排序後：", sortedWeightArr);
        
        //索引權重隨機數的數組下標
        var randomIndex = sortedWeightArr.indexOf(random);    //索引隨機數在新權重數組中的位置
        randomIndex = Math.min(randomIndex, prizes.length -1);    //權重隨機數的下標不得超過獎項數組的長度-1，重新計算隨機數在獎項數組中的索引位置                
        console.log("本次權重隨機數對應的數組下標：", randomIndex);
        
        //取出對應獎項
        res = prizes[randomIndex];    //從獎項數組中取出本次抽獎結果
        console.log("本次抽獎結果：", res);
        
        return {"weightSum": weightSum , "weightRandom": random, prizeIndex: randomIndex, "data": res};    //返回本次抽獎結果
    };

    //註冊按鈕事件
    $('.layui-btn[data-type="save"]').on('click', function () {
        var res = lottery(weightSum);
        document.getElementById("dateNow").innerhtml = util.toDateString(new Date());    //輸出本次抽獎時間
        document.getElementById("weightRandom").innerHTML = res.weightRandom;    //輸出本次抽獎的權重隨機數
        document.getElementById("printData").innerHTML = res.data;    //輸出本次抽獎結果
        
        //重置中獎規則文字的字體顏色    
        $('.rule-body>p').css("color", "inherit");
        $('.rule-body>p:eq(' + res.prizeIndex + ')').css("color", "red");
    });
});